Catalytic converters have been employed to catalyze exhaust fluids in vehicles for more than twenty years and have been manufactured in a number of ways. Catalytic converters play a critical role in ensuring that fuel rich fluids are reduced down to acceptable levels, and are a comparatively expensive article within an exhaust system. The materials are expensive, and manufacture is labor intensive. Furthermore, design packages that increase durability and improve overall system performance for reductions in emissions are at a premium. Accordingly, methods of manufacture have been put forth in attempts to reduce manufacturing costs, while at the same time, increasing durability and stabilizing system performance.
One method of manufacturing catalytic converters is to provide a pre-made canister and stuff it with the catalyst substrate and the insulation/support pad. In this method, the catalyst substrate is wrapped with an intumescent or non-intumescent mat of a selected thickness and weight (various weights are employed for various applications and desired properties). Generally, the wrapped substrate material will create an assembly having outer dimensions that measure about 8 mm larger than the inside dimensions of the converter shell or canister. The assembly as described is then forced through a reduction cone and into the converter shell. Up to about 20,000 lbs of force may be used to accomplish the insertion of the assembly into the can. More particularly, within this range a force up to 7,000 lbs may be used. The method is costly.
A catalytic converter may be produced by a method referred to as “the tourniquet method.” The tourniquet method dispenses with the reducing cone and thus avoids the high insertion pressures on the substrate and mat materials. The method places the substrate and mat assembly into a canister open on one longitudinal edge. The canister is closed around the assembly by straps and compressed to the desired size. The open ends of the canister will, in this position, be overlapping and then are welded together. This method is also expensive and labor intensive. Further, due to this overlap, engineering design consideration must be given to the space alteration inside the canister due to the overlapped edge. The overlapped edge causes a mat density change in the local area of the overlap. This is a further cost addition.
Further, both of the above described catalyst and shell assemblies may have transitional areas to accommodate any difference in diameter between the catalyst shell diameter and the diameter of inlet and outlet pipes. These transitions, e.g., endcones, may be affixed to the shell by Metal Inert Gas (MIG) welding, which may result in a significant amount of cycle time and heat addition to the parts. An alternative to MIG welding is spinforming of the ends of a shell that extends beyond the ends of the catalyst. This process is also high in cycle time and also results in parts having a large area of heated surface. Accordingly, there remains a need in the art for a catalytic converter that is easily and inexpensively manufactured, that increases durability, and does not restrict design choice.